Fix for the invalid Global Proxy Setting

Adding validation for Global Proxy setting before it is
being set.

Proxy is validated at the boot time also to make sure
the value set is valid.

Signed-off-by: Raj Mamadgi <rmamadgi@sta.samsung.com>
bug:11598568

Change-Id: Idff5ae81119d8143da096b5291ecbfbc5875cbd4